free astrology software

Notes on Precision and Calculation Methods

Calculation of Positions of Celestial Bodies

StarFisher uses Swiss Ephemeredes ( and the precision is dependant on these ephemeredes. Generally speaking, the precision is very high, and only in the case of bodies having irregular movement may the precision decrease in the distant past or future.

If you are calculating charts for dates prior to the year 1800 or after 2400, it is recommended that you download and install additional ephemeris files from Downloads. This improves both the speed and precision of the calculations.

Transits and Directions

The transits are calculated so that the maximal error in time is always below 1 second. The method is the same for secondary directions in which the maximal error is approx 365 seconds or 6 minutes (the rule 1 year = 1 day applies to the precision as well).


The geographic data is built from and the time-zone data from The quality is very high but there may be mistakes. Be especially careful when using older dates (prior to WWII) or in the case of places that went through many administrative changes. If you find an inaccuracy or mistake in these data lists, please report it directly to the above mentioned projects. We cannot keep a parallel copy of these databases with any mistakes corrected, rather the main databases need to be fixed.

Composite horoscope

There are multiple methods how to calculate axis in a composite horoscope. StarFisher calculates MC and obliquity and nutation for both charts and makes averages. New ARMC is calculated from the average MC. From these results new axis are calculated.

Risings and settings

The calculations are done for sea level.